The present invention relates to a liquid crystal display device having high display efficiency.
A portable information apparatus as represented by a cellular phone is expected to have multifunction and high grade function while making its communication speed high, thus being needed to accommodate itself to image information of large capacity and is therefore required of high picture quality and ability to perform high definition display. To elaborate on the high picture quality, high contrast, high color reproductivity, wide viewing angle and outdoor legibility can stand for. On the other hand, because of incorporation of various kinds of devices in limited weight and volume, reduced thickness, reduced weight and low power consumption are also required.
The portable information device is used in a variety of environments, in an extremity of bright environment such as direct rays of the sun in the midsummer and in an extremity of dark environment such as a darkroom. For the purpose of obtaining relatively excellent displays throughout the variety of environments, a transflective type liquid crystal display device having a transmissive area and a reflective area within one pixel has been employed frequently.
A white light emitting diode is used as the light source of liquid crystal display device in which emitted blue light is transmitted through a fluorescent material for yellow light emission so that both colors are mixed to produce white color. The liquid crystal display device also has a light absorptive color filter in it. The filter in combination with the liquid crystal display device as an optical shutter, achieves a color display.
Another light absorptive member is also used in the liquid crystal display device and is responsible for reduction in display efficiency of the liquid crystal display device. Among the light absorptive members, a polarization plate and the color filter have high light absorption factors in the extreme but they play a fundamental role in the principle of display in the liquid crystal display device.
In order to improve the display efficiency of liquid crystal display device, various kinds of optical elements have been contrived. In connection with the aforementioned transflective liquid crystal display device, the use of a micro-lens has been thought of. More particularly, in the transflective liquid crystal display device, the area of one pixel is divided into one part for transmissive display and the other major part for reflective display, most of rays of light incident upon which is unusable. Then, it is expected that by concentrating rays of the light source to the transmissive display part through the micro-lens, most of rays of the light source can be utilized efficiently in principle.
Alternatively, the use of color conversion based on fluorescent materials has been considered. In other words, the light source ray is chosen as being ultraviolet light or blue light which can be converted into red, green or blue light by using the fluorescent materials. Subsequently, these rays of light come to or are incident on corresponding color filters, with expectation that the light absorption by the color filter can be reduced in principle. In addition to the fluorescent material, a hologram, for example, is used to separate a ray of white light of light source into its spectral components of red, green and blue which in turn are caused to be incident on corresponding color filters, thereby expectantly attaining a similar effect in principle.
Improvements in display efficiency of the liquid crystal display device based on the micro-lens and hologram are described in JP-A-2003-15121 or JP-A-2003-15122, for example. Improvements in efficiency achieved by converting the blue light from a light emitting diode arranged on the side quarter into red, green and blue rays of light through the uses of the fluorescent material are described in JP-A-2005-353650.